A years-old, one-letter typo led to Aliens: Colonial Marines‘ weird AI

History may never be kind to , but the present tense isn’t looking so good for the lawsuit– and complaint-ridden Gearbox game, either. This week brought to our attention one of the weirdest coding typos we’ve ever seen in a game—which has apparently been hidden inside of ‘s PC version since its 2013 launch.

The first-person shooter returned to gaming’s zeitgeist this week thanks to a 90-percent discount at gaming site Fanatical, which brings its asking price down to $3. (Buying the PC version outright from Steam currently costs the full $30 price.) This sale led one fan to plead with members of the popular gaming forum ResetERA to consider the game as a decent cheap-fun option, especially due to a 712MB fan-made patch at moddb.com that addresses many of the game’s graphical and gameplay glitches.

Tether vs. teather

Upon researching this patch, ResetERA readers noticed something in the moddb.com notes that somehow escaped the gaming community at large in October 2017: the discovery of a one-letter typo in ‘s INI files. As moddb.com user jamesdickinson963 pointed out last year, the game’s “PecanEngine.ini” file references a “tether” system in assigning AI commands to the series’ infamous monsters (which I’ll call “xenomorphs” for brevity’s sake, even though that term isn’t necessarily the right one). However, one of its two mentions of the term “tether” is misspelled as “teather.”

Dickinson’s post alleges that this command, when spelled correctly, “controls tactical position adjustment, patrolling, and target zoning. When a xeno is spawned, it is attached to a zone tether. This zone tells the xeno what area is its fighting space and where different exits are. In combat, a xeno will be forced to switch to a new tether (such as one behind you) so as to flank or disperse so they aren’t so grouped up, etc.” Thanks to how the engine parsed this typo, it never caused any crashes; instead, the engine ignored the unfamiliar term. Thus, the game’s monsters never received the smarter, useful information that had been programmed from the get-go. Instead, they often ran around like in the infamous image below.

This 2017 post came shortly after the release of the group’s final “Game Over, Man!” patch, which, among many other fixes, overwrites this INI file with the typo’s correction. Turns out, as of press time, the patch is still useful. Gearbox has not updated the game’s PC version since July 2013, and the typo is still there.

On Friday, Ars re-downloaded and tested the game, exactly as served by Steam, through the opening beats of two missions. Then, we replayed those missions after editing the “teather” typo in the aforementioned INI file. In both missions, xenomorph AI improved dramatically once the typo was corrected, with monsters immediately taking advantage of elevated attack positions, hiding points, and multi-monster flanks. The difference is night-and-day.

Does this typo-correction upgrade mean the game is officially worth $3? Not necessarily. But the full patch does remedy enough of the game’s biggest issues for anybody who might happen to own the game. Meanwhile, for anybody else in need of a quick sci-fi fix, we can think of worse ways to spend a few bucks for hours of entertainment.

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